As a follow on to a couple of my prior posts ( Hand soldering a VQFN24 part to a PCB and Hand soldering a VQFN24 part to a PCB - part 2 ), this is an update on the progress of that board and a overview on my newly built ISP adapter. In the initial debug stage for this device I had soldered a 2 x 3 header to the board edge while I developed the firmware. As I moved on to my limited production/prototype phase, I wanted to ship the boards without the ISP connector so the device could be fitted into a plastic case. I still wanted a way to attach my debugger/programmer module to the board, so I did a little hacking and came up with a clip-on ISP adapter.
Here is a the top layer pattern that shows the location of the ISP port (J2 along the lower edge of the PCB).
In a prior version of the board, I soldered the ISP connector on to ISP port. Something like this (this is actual a different version of the board):
All along I had envisioned using an old Chip Clip with 0.1" spacing (think DIP clip), but I was planning on building up the contacts on the clip so that the 0.3" width could generate sufficient clamping force to hold the clip onto the board edge. As I started looking more closely at the chip clip, I began to think that I would prefer using the existing contacts and that I would need to remove the travel stops on the chip clip. Here is a side by side view of the modified and standard chip clips:
With the travel stop removed and the contact shrouding cut back you can see the contacts from either side meet in the middle with good spring pressure. Here are a couple views of the clip attached to the PCB:
In the first image, the Debugger/Programmer is shown with the Green LED on, indicating power is properly applied. This second image shows the Pin 1 marker on the clip (Red mark) and the Pin indicator on the PCB (small circle on the connector outline, along with the J2 designation). This clip contacts fit well on the SMT pads. The third image shows the 2 x 3 pin header that I solder onto the chip clip (contacts for power and ground are on the backside of the PCB) and a single wire that connects to the Pin 1 contact (routing for the RST/PGM signal). The ISP module plugs onto this 2 x 3 header.
I built four of the boards using the fixturing from my prior blogs to solder on the ATTINY3227 chips (VQFN-24 with an exposed pad). The soldering process worked out great, the processor attached perfectly on each of the four boards. The rest of the assemble also went well, with the exception of the tiny LEDs (0402 parts - one of which ended up backwards and required some rework). This new board is designed to be a USB to DMX transmitter, that will be used to communicate to the DMX decoders that I build, as my client is currently not able to purchase his prior transmitters due to continued issues with part shortages. This design was a bit tricky as I needed to come up with a module that would communicate with other vendors software and 'look like' an other manufactures product. It took a fair bit of digging to understand the partial exposed API, but I finally figured it out. The first prototype part passed my vendors acceptance test and these new boards will be shipped to selected customers for further testing. I have a couple of changes that I would like to make prior to opening this up for full release.
Thanks for checking this out!
